JP2004536226A - Methods of surface oxidation of zirconium and zirconium alloys and resulting products - Google Patents

Abstract

Uniform and controlled thickness blue-black zirconium oxide coatings on zirconium or zirconium alloy materials are achieved by using single phase crystalline material substrates with altered surface roughness. Uniform and controlled thickness zirconium oxide coatings are used to provide low friction, high wear resistant surfaces to artificial joints such as, but not limited to, hip, knee, shoulder, elbow and spinal implants. It is particularly useful for orthopedic implants of zirconium or zirconium-based alloys. The controlled thickness and uniform thickness of the zirconium oxide surface on the prosthesis provides a barrier to implant erosion caused by ionization of the metal prosthesis. The present invention is also useful for non-articular implants such as bone plates, bone screws, and the like.

Description

【Technical field】
[0001]
Background of the Invention
This application claims priority to US patent application Ser. No. 09 / 909,612, filed Jul. 20, 2001.
[0002]
The present invention relates to a metal implant having a load bearing surface coated with a thin, dense, low friction, high wear resistant, uniform thickness coating of zirconium oxide.
[0003]
The present invention also provides a uniform thickness zirconium oxide on the unloaded support surface of an orthopedic implant in which the zirconium oxide provides a barrier between the metal prosthesis and human tissue, thereby preventing the release of metal ions and corrosion of the implant. Regarding the coating.
[0004]
The present invention also produces a uniform thickness oxide film on zirconium or zirconium alloy by controlling the surface roughness of the zirconium or zirconium alloy having a single phase crystal structure and uniform composition before forming the oxide film. About the method.
[0005]
Zirconium's excellent corrosion resistance has been known for many years. Zirconium exhibits excellent corrosion resistance in many aqueous and non-aqueous media, for which reason its use in the chemical processing industry and medical applications has been increasing. The limitations of the wide application of zirconium in these areas are relatively low wear resistance and propensity to wear. This relatively low wear resistance and propensity to wear are also exhibited in zirconium alloys.
[0006]
Orthopedic implant materials must combine high strength, corrosion resistance and histocompatibility. The life of the implant is most important, especially if the recipient of the implant is relatively young, as it is desirable for the implant to function for the entire life of the patient. Certain metal alloys have the required mechanical strength and biocompatibility and are therefore ideal candidates for the manufacture of prostheses. These alloys include 316L stainless steel, a chromium-cobalt-molybdenum alloy, and more recently a titanium alloy that has proven to be optimal for the manufacture of load-bearing prostheses.
[0007]
One of the variables that determines the longevity of a load-bearing implant is the rate of wear of the articular surface and the long-term effects of metal ion release. A typical hip prosthesis comprises a stem, a femoral head, and an acetabular cup with which the femoral head forms an articulation. Wear of one or both of the articular surfaces increases wear particle levels and creates "play" between the thigh head and the cup articulated to it. The joints must eventually be replaced because the wear debris acts to prevent tissue rejection from leading to bone resorption.
[0008]
The rate of wear depends on many factors, including the relative hardness and surface finish of the materials that make up the femoral head and acetabular cup, the coefficient of friction between the material of the cup and the head, the applied load. Includes stresses that occur on joint surfaces. The most common material combination currently used in the manufacture of hip implants is for acetabular cups lined with organic polymers or composites such as, for example, polymers including ultra high molecular weight polyethylene (UHMWPE). Includes an articulated femoral head of cobalt or titanium alloy and an abrasive alumina thigh head lined with an organic polymer or composite or bonded to an acetabular cup made of abrasive alumina.
[0009]
Among the factors affecting the wear rate of conventional hip implants, the most important are the patient's weight and activity level. In addition, it has been shown that frictional heat during normal use of the implant, such as during walking, accelerates the creep and wear of the polyethylene cup. Furthermore, there is a correlation between the frictional moment transmitting the torque load to the cup and the coefficient of friction between the femoral head and the surface of the acetabular cup that articulates the head. Cup torque has been associated with cup loosening. Thus, in general, the higher the coefficient of friction for a given load, the higher the level of generated torque. Ceramic bearing surfaces have been shown to produce significantly lower levels of friction torque.
[0010]
Of note, as noted above, two of the three commonly used hip systems include a metal thigh head articulated against the lining of the UHMWPE in the acetabular cup. UHMWPE is a polymeric material that, when heated, is more susceptible to creep than commonly used metal alloys or ceramics due to its relatively low melting point, and is therefore more prone to wear than alloys and ceramics.
[0011]
It has also been found that metal prostheses are not necessarily inert in the human body. Body fluids act on metals, causing them to slowly erode by ionization, thereby releasing metal ions into the body. The metal ions released from the prosthesis are also related to the rate of wear of the load bearing surface. This is because the passivating oxide film formed on the surface is always removed. Its re-passivation action always releases metal ions during the ionization action. In addition, the presence of abrasives (cement or bone debris) accelerates this effect, and fine corroded metal particles increase wear. As a result, the UHMWPE lining in the acetabular cup is articulated against the femoral head and is subjected to accelerated levels of creep, wear and torque.
[0012]
Suzuki et al., U.S. Pat. No. 4,145,764, recognizes that metal prostheses have excellent mechanical strength but tend to corrode in the body by ionization. Suzuki et al. Also noted the affinity between ceramics and bone tissue, but noted that ceramic prostheses had poor impact resistance. Accordingly, Suzuki et al. Provided a metal prosthesis that was sequentially sprayed with a porous cement coating that was plasma sprayed with an adhesive and allowed to ingrow the bone into the pores. This combination, as already mentioned, will provide both the mechanical strength of the metal and the biocompatibility of the ceramic.
[0013]
The Suzuki patent did not address the friction and wear issues of orthopedic implants, but focused on a single issue on the biocompatibility of metal prostheses. In addition, Suzuki et al. Did not address the issues of dimensional changes that occur when applying a coating or the effects of dimensional changes in the reduction of the fit between the prostheses that form the joint.
[0014]
In addition, applying a ceramic coating to a metal substrate often results in a non-uniform, poorly adherent coating that tends to crack due to differences in elastic modulus and thermal expansion between the ceramic and the underlying metal substrate. . In addition, such coatings tend to be relatively thick (50-300 microns), the adhesion between the metal and the ceramic coating is often weak, and there is a risk of wear and flaking of the ceramic coating.
[0015]
It has long been attempted to create a zirconium oxide coating on zirconium components to increase wear resistance. One such process is disclosed in Watson U.S. Pat. No. 3,615,885, which deploys a thick (up to 0.23 mm) oxide layer over Zircaloy 2 and Zircaloy 4. To disclose the procedure. However, this procedure results in significant dimensional changes for parts having a thickness of about 5 mm or less, and the oxide films formed do not show particularly high wear resistance.
[0016]
Watson U.S. Pat. No. 2,987,352 discloses a method for producing a blue-black oxide coating on a zirconium alloy part with the goal of increasing wear resistance. Both U.S. Pat. No. 2,987,352 and U.S. Pat. No. 3,615,885 produce a zirconium oxide coating on a zirconium alloy by air oxidation. U.S. Pat. No. 3,615,885 continues air oxidation long enough to produce a thicker beige coating than the blue-black coating of U.S. Pat. No. 2,987,352. This beige coating does not have the abrasion resistance of a bluish black coating and is not applicable to many parts with two working surfaces in close proximity. Due to the resulting formation of zirconium oxide particles and loss of integrity of the zirconium oxide surface, the beige coating wears faster than the blue-black oxide coating. Loss of the oxidized surface exposes the zirconium metal to the environment and moves the zirconium interface from the metal surface to the adjacent environment.
[0017]
The hardness of the blue-black coating is higher than that of the beige coating, but the blue-black coating has a smaller thickness than the beige coating. This hard blue-black oxide coating works well on surfaces such as prostheses. The blue-black coating is more abrasion-resistant than the beige coating, but is a relatively thin coating. Accordingly, it is desirable to produce a highly abrasive blue-black coating without producing the same type of coating as in the prior art.
[0018]
U.S. Pat. No. 5,037,438 to Davidson discloses a method for making a zirconium alloy prosthesis having a zirconium oxide surface. U.S. Pat. No. 2,987,352 to Watson discloses a method of making a zirconium bearing having a zirconium oxide surface. Since the oxide film produced is not necessarily uniform in thickness, its non-uniformity reduces the integrity of the bond between the zirconium alloy and the oxide layer and the integrity of the bond within the oxide layer. U.S. Pat. Nos. 2,987,352 and 5,037,438 are incorporated by reference as if fully set forth herein.
[0019]
In International Publication No. PCT WO 98/42390 and related US Ser. No. 09 / 381,217, Hunter et al. Disclosed a method for obtaining a zirconium oxide coating of uniform thickness. Hunter has shown that it can be obtained by applying nominal oxidation techniques to substrate materials that result in a refined microstructure and variable surface roughness. Microstructure refining is shown in PCT WO 98/42390 by techniques including hot forging of ingots into wrought bars, closed die forging, rapid solidification and powder compaction. Variable surface roughness is achieved by grinding, buffing, mass finishing, vibratory finishing, and the like. US application Ser. No. 09 / 381,217 is incorporated by reference as if fully set forth herein.
[0020]
There is a need for a method of forming a uniform thickness oxide film on a zirconium alloy. There is a need for a metal alloy based orthopedic implant having a low friction, high wear resistant load bearing surface that can be implanted for the life of a recipient. There is a need for a metal alloy-based orthopedic implant that is less susceptible to corrosion by the action of bodily fluids, is biocompatible, and is stable for the life of the recipient.
[0021]
The present invention induces an altered surface roughness on a single-phase / single-composition zirconium-based substrate prior to oxidizing the zirconium or zirconium alloy to form a blue-black zirconium oxide coating of uniform and controlled thickness. It is another object of the present invention to provide an improved method for forming an oxide film having a uniform thickness on zirconium or a zirconium alloy having a single-phase crystal structure and a uniform composition. The present invention also alters the surface roughness of at least a portion of a zirconium or zirconium alloy prosthesis, wherein the zirconium or zirconium oxide at least partially includes a single phase crystal structure and uniform composition prior to oxidizing the prosthesis. Forming a uniform and controlled thickness of a blue-black zirconium oxide coating on at least a portion of the surface of the prosthesis with a uniform thickness oxide coating on a zirconium or zirconium alloy prosthesis for implantation in a patient. It provides a method of forming.
[0022]
Summary of the invention
“One” as used in the following description means one or more. When used in the claims, in connection with "comprising", "one" means one or more. “Other” as used below means at least a second or more.
[0023]
As used herein, the term "single-phase crystal structure and homogeneous composition" is defined as an alloy or pure metal material having a homogeneous, solid solution, microstructure with only one crystalline phase. In the case of an alloy, it refers to a single homogeneous solid solution in which the entire metal consists of only a single crystalline phase.
[0024]
As used herein, "zirconium alloy" is defined as any metal alloy containing zirconium in an amount greater than zero. Therefore, here, an alloy having a small amount of zirconium is considered as a “zirconium alloy”.
[0025]
The following description includes examples of preferred embodiments for practicing the present invention. However, they are not limiting examples. Other examples and methods are possible in practicing the invention.
[0026]
The present invention relates to a prosthesis or implant of zirconium or a zirconium-containing metal alloy coated at least in part through natural oxidation with a blue-black or black layer of uniform thickness of zirconium oxide and a method of forming the uniform coating. provide. Uniform coatings of zirconium oxide provide a thin, dense, low-wear, wear-resistant, biocompatible surface ideally suited for use on articular surfaces of joint prostheses. Provide a prosthesis that articulates, moves, and rotates with respect to a surface coated with zirconium oxide. Thus, a uniform zirconium oxide coating may be used for femoral heads, the inner surface of acetabular cups of hip implants, and other types such as, but not limited to, knee, shoulder, upper, elbow or spinal implants. Useful for articulating surfaces of prostheses.
[0027]
One embodiment includes modifying the surface roughness of a zirconium or zirconium alloy having a single phase crystal structure and a single composition, and then oxidizing the zirconium or zirconium alloy, comprising a bluish black or black of uniform thickness. There is a method of coating zirconium or a zirconium alloy with a layer of black zirconium oxide. In one particular embodiment, the step of changing the surface roughness comprises changing the surface roughness (Ra) in a range from about 3 microinches to 25 microinches. In another embodiment, the step of changing the surface roughness comprises changing the surface roughness (Ra) in a range from about 3.5 micro inches to 7 micro inches. Changing the surface roughness can be achieved in a number of ways. Examples of altering the surface roughness include, but are not limited to, grinding, buffing, mass finishing, shaking finishing, and any combination thereof. In a specific embodiment of the method, zirconium or a zirconium alloy having a particle size smaller than ASTM micro particle size number 10 is used. Oxidation of zirconium or a zirconium alloy can be achieved in a number of ways. Examples include, but are not limited to, using air as the oxidant and using oxygen as the oxidant. In certain embodiments, altering the surface roughness of the zirconium or zirconium alloy having a single phase crystal structure and uniform composition is performed on a zirconium or zirconium alloy containing 0.3% by weight oxygen. In yet another embodiment, the method includes altering the surface roughness of pure alpha phase zirconium. Zirconium or zirconium alloys are manufactured in a number of ways. Examples include, but are not limited to, processes selected from the group including hot forging of ingots into bars, closed die forging, rapid solidification, and powder compaction.
[0028]
In another embodiment of the invention, a prosthesis body having an outer surface at least a portion of which is formed from zirconium or a zirconium alloy, and a uniform thickness bluish black or black oxide formed over said portion of the outer surface There is a prosthesis comprising a zirconium coating and implanted in a patient. The blue-black or black zirconium oxide is formed by any of the methods described above, or any equivalent method.
[0029]
In certain embodiments, the prosthesis is a non-articulated medical device in which the prosthesis body is at least partially formed from a zirconium or zirconium alloy material comprising a partially or completely coated blue-black or black zirconium oxide of uniform thickness. It is an implant. In another particular embodiment, the non-articular medical implant is selected from the group comprising bone plates and bone screws.
[0030]
In another embodiment, a prosthesis having a support surface includes at least one condyle on the prosthesis body and a tibial element adapted to cooperate with the support surface. The blue-black or black zirconium oxide coating forms directly on the bearing surface of the condylar region and reduces wear of the tibial component. In this embodiment, the tibial component can be formed from an organic polymer or a polymer-based composite. In another embodiment, the prosthesis further comprises a support surface on the prosthesis body, the support surface having a size and shape to engage or cooperate with the second support surface of the other prosthesis portion. it can. In certain embodiments, the second support surface is formed from an organic polymer or a polymer-based composite.
[0031]
In yet another embodiment of the present invention, the prosthesis body is a hip prosthesis for implantation in a femur with a head formed from zirconium or a zirconium alloy. In this embodiment, the prosthesis comprises a support surface on the head of the prosthesis body and an acetabular cup having an inner surface, the inner surface cooperating with the support surface on the head. . The coating of blue-black or black zirconium oxide is formed directly on the support surface of the head portion to reduce wear on the inner surface of the acetabular cup. In certain embodiments, the inner surface of the acetabular cup can be formed from an organic polymer or a polymer-based composite.
[0032]
In other embodiments, any of the foregoing prostheses is characterized in that the blue-black or black zirconium oxide coating is up to about 20 microns or up to about 10 microns thick.
[0033]
In another embodiment, any of the foregoing prostheses, the implanted portion of the prosthesis body further comprises an irregular surface structure adapted to receive tissue that grows in a portion of the prosthesis body. It is characterized by. In certain embodiments, the irregular surface structure is formed from zirconium or zirconium metal beads attached to the outer surface of the prosthesis body, and at least a portion of the surface of the beads is oxidized to a blue-black or black zirconium oxide. Has become. The irregular surface structure is formed of a metal mesh of zirconium or a zirconium alloy connected to the outer surface of the prosthesis body, and at least a part of the mesh is oxidized to bluish black or black zirconium oxide.
[0034]
In other embodiments, any of the foregoing prostheses is characterized in that the prosthesis body is an endoprosthesis body suitable for a knee, hip, jaw, finger, scapula, or spinal cord.
[0035]
Description of the drawings
FIG. 1 is a schematic diagram showing the hip prosthesis in the correct position.
[0036]
FIG. 2 is a schematic view showing a general hip joint prosthesis.
[0037]
FIG. 3 is a schematic diagram showing the hip joint prosthesis in the correct position.
[0038]
FIG. 4 is a schematic view showing a general knee joint component.
[0039]
Detailed description of the invention
One aspect of the present invention is to provide a method of forming a uniform thickness oxide film on zirconium or zirconium alloy having a single phase crystal structure and a uniform composition and a modified surface roughness, respectively. Another aspect of the invention is a low-profile, uniform thickness over a prosthetic surface, such as an articulated and irregular surface structure adapted to accommodate tissue ingrowth in a portion of the prosthetic body. The purpose is to provide an oxide film for friction.
[0040]
The main method of forming a uniform thickness oxide film by inducing an altered surface roughness on a zirconium or zirconium alloy having a single phase crystal structure and a uniform composition, respectively, before oxidizing the zirconium or zirconium alloy Can be applied to various prosthetic parts and devices. These prosthetic components and devices include heart valves, total prosthetic heart implants, ventricular assist devices, cardiovascular implants including vascular grafts and stents; electrical devices such as pacemakers, neural inductors and defibrillation inductors. Signal transmission devices; guidewires and catheters; percutaneous devices; and joint prostheses, including, but not limited to, hip and surface replacements, knees, back, elbows, endoprostheses, spinal segments and fingers . Examples of such articulating surfaces are shown in the schematic diagrams of FIGS. Further, the present invention is applicable to non-articular implant elements such as bone plates and bone screws.
[0041]
A representative hip joint assembly is shown in a natural position in FIG. The hip stem 2 is fitted in the femur, and the femoral head 6 of the prosthesis is fitted in the inner layer 8 of the acetabular cup 10 which is fixed to the pelvis in order as shown in FIG. Porous metal beads or wire mesh coating 12 is incorporated to stabilize the implant by ingrowth of surrounding tissue into the porous coating. Similarly, such porous metal beads or wire mesh coatings can be applied to the acetabular component. The thigh head 6 may be an integral part of the hip stem 2 or may be a separating element mounted on a conical taper at the end of the neck 4 of the hip prosthesis. This allows the fabrication of a prosthesis with a metal stem and neck, rather than a thigh head of another material such as ceramic. This method of construction is often desirable. This is because ceramics were found to produce little friction torque and friction when articulating with the UHMWPE lining of the acetabular cup. In addition, zirconia ceramics have been found to wear UHMWPE less than alumina. However, regardless of the material, the femoral head articulates with the inner surface of the acetabular cup, thereby causing wear, and over time, this may require replacement of the prosthesis. This is especially the case when the femoral head is metal and the acetabular cup is lined with an organic polymer or a composite thereof. Although polymer surfaces provide good, relatively low friction surfaces and biocompatibility, they are subject to wear and accelerated creep due to the frictional heat and torque experienced during normal use.
[0042]
Although UHMWPE cross-linked through irradiation followed by a heating step has been shown to exhibit great abrasion resistance, it has similar disadvantages. A representative knee prosthesis in natural position is shown in FIG. The knee joint comprises a thigh element 20 and a tibial element 30. The femoral component comprises a condyle 22 with the articular surface of the femoral component and a nail 24 for fixing the femoral component to the femur. The tibial component 30 includes a tibial base 32 having a nail 34 for mounting the tibial base on the tibia. The tibial platform 36 includes a groove 38 mounted on the tibial base 32 and resembling the shape of the condyle 22. The bottom surface of the condyle 26 contacts the grooves 38 of the tibial platform, and the condyles articulate in these grooves to the tibial platform. The condyles are typically made of metal, while the tibial platform can be made of an organic polymer or polymer-based composite. Thus, the hard metal condylar surface 26 articulates with the relatively soft organic composition. This results in wear of the organic material, the tibial platform, and requires replacement of the prosthesis. As in the case of the hip joint, a porous bead or wire mesh covering can be applied to the tibial or thigh element or both of the knee joint.
[0043]
The present invention provides orthopedic implants or prostheses comprised of zirconium or a zirconium-containing metal alloy and coated with a uniform thickness of zirconium oxide, or a thin coating of zirconium or a zirconium alloy of conventional orthopedic implant materials. In order to form a continuous and useful uniform thickness zirconium oxide coating on the desired surface of the metal alloy prosthesis substrate, the metal alloy is present in an amount of about 80 to about 100% by weight, preferably about 94 to about 100% by weight. Should contain zirconium. Oxygen and other common alloy elements may be used in the alloy if the resulting alloy is of a single phase. The oxygen, nitrogen, and carbon of the interstitial elements have the ability to strengthen zirconium, particularly while maintaining a single-phase crystalline microstructure. At low temperatures, zirconium is an alpha (α) phase crystal. Beta (β) phase zirconium is stable at high temperatures (above about 866 ° C.), but can be made stable at low and high levels by adding β stabilizers such as niobium (α stabilizers such as oxygen). Increases the transition temperature). Examples of useful alloys in this application are α-phase zirconium containing 0.3% by weight of oxygen, α-phase stabilizer. Other alpha phase stabilizers include nitrogen, aluminum, and tin. Also, beta phase zirconium alloyed with one or more beta stabilizers such as niobium, chromium, iron and molybdenum is useful in the present invention.
[0044]
The base zirconium-containing metal alloy is made by conventional methods into the desired shape and size to provide the prosthetic substrate. Shaped zirconium or zirconium alloys must have a single-phase crystalline structure and uniform composition made by alloying zirconium with one or more other elements to make a single-phase alloy material.
[0045]
Next, the zirconium or zirconium alloy of the substrate is subjected to a surface polishing treatment including, but not limited to, grinding, buffing, mass finishing and vibration finishing. The surface polishing process is used to create a modified surface roughness of about 3 to about 25 microinches. Also, the range of the surface roughness can be from about 3.5 to about 7 microinches. When zirconium or a zirconium alloy is subjected to an oxidation treatment with a single-phase crystalline structure and uniform composition, respectively, and a moderately changed surface roughness, the appropriate changed surface roughness will reduce the pre-existing surface roughness. By varying the surface roughness to a size that can form a uniform oxide film.
[0046]
Next, the substrate is subjected to processing conditions that allow the spontaneous (natural) formation of a tightly adhered, diffusion bonded coating of zirconium oxide of uniform thickness on its surface. The processing conditions include, for example, air, steam, hydroxylation or salt bath oxidation. These processes are thin, hard, dense, blue-black or black, low-friction, abrasion-resistant, uniform-thickness zirconium oxide films or coatings, typically in the range of a few microns. Is ideally provided on the surface of the prosthesis substrate. Oxygen diffused under the coating by oxidation increases the hardness and strength of the underlying base metal.
[0047]
The oxidation of air and water is described in expired Watson U.S. Pat. No. 2,987,352, the disclosure of which is incorporated by reference as if set forth. Oxidation treatment applied to zirconium or zirconium alloy, each having a single-phase crystalline structure, uniform composition and moderately varying surface roughness, firmly adheres zirconium oxide of uniform thickness of highly stretched monoclinic crystal type To provide a black or blue-black layer. If the oxidation is continued excessively, the coating becomes white and separates from the metal substrate. For convenience, the metal prosthesis substrate is placed in a furnace having an oxygen-containing atmosphere, such as air, and is typically heated at 900 ° -1300 ° F. for up to about 6 hours. However, other combinations of temperature and time are possible. Using higher temperatures reduces the oxidation time and prevents the formation of white oxides.
[0048]
One salt bath method that can be used to apply a zirconium oxide coating to a metal alloy prosthesis is that of Hagers U.S. Pat. No. 4,671,824, the disclosure of which is fully incorporated herein by reference. Incorporated by citation. The salt bath method provides a similar, somewhat abrasion-resistant blue-black or black zirconium oxide coating. This method requires that an oxidizing compound capable of oxidizing zirconium be present in the molten salt bath. The molten salt contains chloride, nitrate, cyanide and the like. The oxidizing compound, sodium carbonate, is present at slightly up to about 5% by weight. The addition of sodium carbonate lowers the melting point of the salt. As in air oxidation, the rate of oxidation is proportional to the temperature of the molten salt bath, and the '824 patent prefers a range of 550 ° C to 800 ° C (1022 ° F to 1470 ° F). However, the low oxygen level in the salt bath produces a thinner film than furnace air oxidation at the same time and at the same temperature. A 4 hour salt bath treatment at 1290 ° F. produces an oxide coating thickness of about 7 microns.
[0049]
The overall thickness of the zirconium oxide coating is mainly controlled by various times and temperatures in the native growth process. The invention relates to the uniformity of the thickness of the coating so produced. The formation of a uniform oxide film during the oxidation treatment according to the method described herein depends on the surface having a suitably varied surface roughness, the single-phase crystalline structure and the uniform composition. Since the oxide film grows starting from the unevenness of the surface, if the oxidation start site is too far away, a uniform coating thickness is formed on the surface that is too smooth. Oxidation rates can be different in grains of different structure and composition (such as between alpha and beta grains in a two-phase zirconium alloy). Therefore, the oxide film may not grow to a uniform thickness due to a microstructure that is too coarse. Specific limits on the required minimum surface roughness and maximum phase homogeneity depend on the alloy and the application.
[0050]
Uniform thickness zirconium oxide coatings vary up to about 20 microns. Preferably, a blue-black zirconium oxide layer of uniform thickness varying from about 1 to about 10 microns in thickness is formed. Most preferably, the uniform thickness zirconium oxide layer varies from about 3 microns to about 7 microns. For example, furnace air oxidation at 1100 ° F. for 3 hours can produce a 4-5 micron thickness over a zirconium alloy having a surface roughness (Ra) of about 4 microinches and having more than 96% by weight zirconium. To form a uniform oxide film. Longer oxidation times and higher oxidation temperatures increase this thickness, but can jeopardize the integrity of the coating. For example, 1300 ° F. for 1 hour forms an oxide coating thickness of about 9 microns. Of course, only a very small dimensional change, typically less than 10 microns over the thickness of the prosthesis, results, since only a thin oxide is required for the surface. Generally, thin coatings (1-10 microns) have good adhesion strength. However, depending on the application, a thicker coating may be used.
[0051]
Blue-black or black zirconium oxide coatings produced by any of the prior art methods are quite similar in hardness. For example, when a polished zirconium alloy prosthesis substrate is oxidized, the surface hardness shows a dramatic increase over the initial 200 Knoop hardness of the metal surface. The surface hardness of the blue-black zirconium oxide surface resulting from the salt bath or air oxidation treatment is about 1200-1700 Knoop hardness.
[0052]
The diffusion bonded, low friction, high wear resistant, uniform thickness zirconium oxide coating of the present invention provides a device that requires prosthetic surfaces, orthopedic implants, and biocompatible surfaces to be exposed to wear conditions. Applicable to Such surfaces include the knee, elbow and hip joint surfaces. As described above, in the case of a hip joint, the femoral head and stem are typically made of a metal alloy, and the acetabular cup is made of ceramics, metal, or a metal or ceramic lined with an organic polymer. Is done.
[0053]
When a zirconium oxide coating is applied to a surface that is subject to wear, it is desirable to obtain a smooth finished surface to minimize wear. After the oxidation treatment, the oxide surface can be polished by any of a variety of conventional finishing techniques. Sufficient oxide thickness must be formed to accommodate the selected finishing technique. For example, a surface having a uniform oxide layer of about 5 microns, which had a surface roughness (Ra) of about 4 micro inches prior to oxidation, can be reduced to about 2 microns by reducing the oxide thickness by about 1 micron. It can be polished to a final surface roughness (Ra) of inches.
[0054]
Zirconium or zirconium alloys can also be used to provide porous beads or metal mesh surfaces, with which the surrounding bone and other tissues integrate to stabilize the prosthesis. These porous coatings can be simultaneously treated by oxidation of the prosthetic substrate to eliminate or reduce metal ion emissions. In addition, zirconium or a zirconium alloy can also be used as a surface layer applied over conventional implant materials prior to the introduction of variable surface roughness, natural oxidation and formation of a uniform zirconium oxide coating.
[0055]
The problem of forming a thick oxide film with low abrasion and with large dimensional changes in the process of US Pat. No. 3,615,885 is avoided by the process of the present invention. Controlling both the overall coating thickness and thickness uniformity allows for many dimensional controls in the manufacture of prostheses where tight tolerances are required. The present invention also produces an oxide film having high abrasion resistance, unlike that of the '885 patent.
[0056]
The treatment of the present invention creates a uniform thickness blue-black zirconium oxide coating by producing a variable surface roughness on zirconium or zirconium alloy having a single phase crystal structure and uniform composition, and having a thickness of Can be controlled by appropriately selecting the oxidation conditions. By forming an oxide film having a uniform thickness, it has particularly high wear resistance and low wear due to the high integrity of the adhesion between the oxide film and the underlying zirconium or zirconium alloy and the high integrity of the adhesion in the oxide layer. An oxide coating of variable and controllable thickness is provided. The term "high integrity" refers to a uniform oxide film of thickness without visible cracks or holes when viewing the cross section with an optical microscope.
[0057]
The present invention provides a prosthesis made of zirconium or a zirconium-containing metal alloy having a single phase crystal structure and a uniform composition coated with natural oxide by a uniform thickness of zirconium oxide. Zirconium oxide coatings of uniform thickness provide a thin, dense, low-friction, high-integrity joint ideally used for articulating surfaces of moving and rotating joint prostheses where the articulating surface is articulated to the corresponding articulating surface. A prosthesis of the invention having a wear-resistant, biologically applicable surface. Thus, zirconium oxide coatings of uniform thickness are usefully used on femoral heads, on the inner surface of acetabular cups of hip implants, and on the articulating surfaces of other types of prostheses, such as knee joints.
[0058]
When a joint surface coated with a uniform thickness of zirconium oxide is used to articulate or rotate with respect to a surface coated with a non-metallic or non-zirconium oxide, a uniform thickness Due to the low friction properties of the coating and the high integrity of the uniform thickness coating, friction, wear and heat generation are reduced relative to prior art prostheses. This reduced heat generation reduces the tendency of the non-metallic or non-zirconium oxide coated support surface to experience creep and torsional moments and increases the useful life of the opposing surface. Organic polymers such as UHMWPE rapidly increase the rate of creep when exposed to heat that has a detrimental effect on the lifetime of the inner layer. Polymer debris can lead to adverse tissue reactions and loosening of the appliance. Thus, a uniform thickness zirconium oxide coating not only helps to improve the protection of the prosthesis substrate to which it is applied with high integrity, but it also makes it in operative contact as a result of its low friction surface It protects these surfaces and consequently increases the performance and longevity of the prosthesis.
[0059]
Uniform thickness zirconium oxide coated articular surfaces also increase the useful life of the opposing surface when the opposing surface is human tissue. Surgical replacement of one element of a joint is referred to as "hemiarthroplasty", and since the replaced joint has only one joint (prosthesis) element, the joint element is a "monopolar" prosthesis. Or, it is often referred to as "endoprosthesis." The uniform thickness of the zirconium oxide coating is a low friction surface for articulating, moving, and rotating with respect to the body tissue, thereby reducing the case where the organic polymer is opposed to the opposed surface of the organic polymer. And produce similar beneficial results.
[0060]
The usefulness of zirconium oxide coated prostheses is not limited to load bearing prostheses, especially to joints that experience high speed wear. Other applications are possible in non-articular implant devices such as bone plates and bone screws. The uniform thickness of the zirconium oxide coating is tightly adhered to the zirconium alloy prosthesis substrate, thus providing a reinforced boundary wall between bodily fluids and the zirconium alloy metal, thereby providing ionization and associated metallization. Corrosion of the alloy due to the process of ion release is prevented as compared with the non-uniform oxide film.
[0061]
Further, spontaneous formation of a uniform thickness zirconium oxide coating from the presence of zirconium in the substrate metal includes diffusing oxygen into the metal substrate under the oxide coating. Oxygen, which is an alloying component in zirconium, increases the strength of the metal substrate, particularly the fatigue strength. In addition, the high integrity of a uniform thickness coating reduces the number of fatigue crack initiation sites for non-uniform thickness oxide films including cracks and holes. Resistance to fatigue loading is excellent in many orthopedic implant applications such as hip stems and femoral and tibial knee components. Thus, the formation of a zirconium oxide coating of uniform thickness not only improves wear, friction and corrosion resistance, but also improves the mechanical integrity of the implant device from a strength standpoint.
[0062]
Although the present invention has been described with reference to preferred embodiments thereof, those skilled in the art, upon reading this disclosure, will appreciate that modifications and variations that can be made without departing from the scope and spirit of the invention described above or below. Can be recognized.
[0063]
All patents and publications mentioned in the specification are indicative of the levels of those skilled in the art to which this invention pertains. All patents and publications are herein incorporated by reference to the same content as if each publication were specifically indicated to be individually incorporated by reference.
U.S. Patent Literature
4,145,764 3/1979 Suzuki and others
3,615,885 10/1971 Watson
2,987,352 6/1961 Watson
5,037,428 8/1991 Davidson
Foreign patent literature
PCTWO98 / 42390 10/1998 (issued) Hunter and others
Other references
ASTM Manual on Zirconium and Hafnium, Jay. H. Schmel, Special Technical Publication 639, American Society for Testing and Materials, Philadelphia, PA, 1977.
Transformations in Metals, P. Gee. Seuman, McGraw-Hill, New York, 1969.
[0064]
Those skilled in the art will readily recognize that the present invention may be well adapted to carry out the objects and obtain the described results and advantages, as if they existed. The systems, methods, procedures, and techniques described herein represent presently preferred embodiments, are intended to be illustrative, and not limiting. Variations and other uses that fall within the spirit of the invention or are defined by the claims will occur to those skilled in the art.
[Brief description of the drawings]
[0065]
FIG. 1 is a schematic diagram showing the hip prosthesis in the correct position.
FIG. 2 is a schematic view showing a general hip joint prosthesis.
FIG. 3 is a schematic diagram showing the knee joint prosthesis in the correct position.
FIG. 4 is a schematic view showing a general knee joint part.

Claims (24)

Changing the surface roughness of the zirconium or zirconium alloy having a single phase crystal structure and a single composition, and then oxidizing the zirconium or zirconium alloy, the zirconium by a layer of blue-black or black zirconium oxide of uniform thickness. Alternatively, a method of coating a zirconium alloy. The method of claim 1 wherein the step of changing the surface roughness comprises changing the surface roughness (Ra) in a range from about 3 microinches to 25 microinches. The method of claim 1 wherein the step of changing the surface roughness comprises changing the surface roughness (Ra) in a range from about 3.5 micro inches to 7 micro inches. 2. The method of claim 1, wherein the step of changing the surface roughness comprises a polishing surface preparation process comprising a step selected from the group comprising grinding, buffing, mass finishing, shaking finishing, and any combination thereof. Method. The method of claim 1, wherein the zirconium or zirconium alloy has a grain size less than ASTM micro grain size number 10. The method of claim 1, wherein the oxidizing step uses air as an oxidant. The method of claim 1, wherein the oxidizing step uses oxygen as an oxidant. Altering the surface roughness of the zirconium or zirconium alloy having a single phase crystal structure and uniform composition comprises altering the surface roughness of the zirconium or zirconium alloy having about 0.3% oxygen by weight. The method of claim 1. The method of claim 1 wherein the step of changing the surface roughness of zirconium or a zirconium alloy having a single phase crystal structure and uniform composition comprises changing the surface roughness of pure alpha phase zirconium. The method of claim 1, further comprising the step of producing zirconium or a zirconium alloy by a process selected from the group comprising hot forging of ingots into bars, closed die forging, rapid solidification, and powder compaction. (A) a prosthesis body having an outer surface at least a portion of which is formed from zirconium or a zirconium alloy;
(B) a blue-black or black zirconium oxide coating of uniform thickness formed on said portion of the outer surface;
A prosthesis for implantation in a patient, comprising a blue-black or black zirconium oxide coating formed by the method of any one of claims 1 to 10. (A) a support surface comprising at least one condyle on the prosthesis body;
(B) a tibial element adapted to cooperate with the bearing surface;
12. The prosthesis of claim 11, further comprising a blue-black or black zirconium oxide coating formed directly on the bearing surface of the condylar portion to reduce wear of the tibial component. 13. The prosthesis of claim 12, wherein the tibial component is formed from an organic polymer or a polymer-based composite. A prosthesis body is a hip joint prosthesis body that is implanted into a femur with a head portion formed of zirconium or a zirconium alloy, wherein the prosthesis is
(A) a support surface on the head of the prosthesis body,
(B) an acetabular cup having an inner surface adapted to cooperate with a support surface on the head portion;
12. The prosthesis of claim 11, further comprising: a blue-black or black zirconium oxide coating formed directly on the support surface of the head to reduce wear on the inner surface of the acetabular cup. 15. The prosthesis of claim 14, wherein the inner surface of the acetabulum is formed from an organic polymer or a polymer-based composite. 12. The prosthesis of claim 11, further comprising a support surface on the prosthesis body, the support surface having a size and shape to engage or cooperate with a second support surface on another prosthesis portion. 17. The prosthesis of claim 16, wherein the second support surface is formed from an organic polymer or a polymer-based composite. 17. The prosthesis of any of claims 11 to 16, wherein the blue-black or black zirconium oxide coating is up to about 20 microns or up to about 10 microns thick. 17. The prosthesis of any of claims 11-16, wherein the implanted portion of the prosthesis further comprises an irregular surface structure adapted to accommodate tissue ingrowth on a portion of the prosthesis body. The irregular surface structure is formed of zirconium or zirconium alloy beads attached to the outer surface of the prosthesis body, and a part of the surface of the beads is oxidized to blue-black or black zirconium oxide. Item 20. The prosthesis of Item 19. The irregular surface structure is formed from a wire mesh of zirconium or a zirconium alloy connected to the outer surface of the prosthesis body, and a part of the surface of the wire mesh is oxidized to blue-black or black zirconium oxide. 20. The prosthesis of claim 19, wherein 22. The prosthesis of any of claims 11, 18, 19, 20 and 21, wherein the prosthesis body is an endoprosthesis body suitable for use on a knee, hip, chin, finger, shoulder, or spine. 12. The implant of claim 11, wherein the prosthesis body is a non-articular medical implant at least partially formed from a zirconium or zirconium alloy material with a partial or complete coating of blue-black or black zirconium oxide of uniform thickness. Prosthesis. 24. The medical implant of claim 23, selected from the group consisting of a bone plate and a bone screw.